the OD relay has two output pins that are wired together, and are either conneccted to power or to ground. the OD light is wired to power and the relay, so it lights when the relay is grounding. the OD solenoid is wired to ground and the relay, so its powered when the relay is powered, and the light is out.

yup, light on == no OD solenoid. light off == OD solenoid. fun, eh?

when the OD solenoid is powered, OD is enabled and the car will shift to 4th automatically as needed. if you're cruising down the road at a steady 45mph and push the button do you feel the gearbox shifting, and the RPMs change? or, accelerate very gently from a start with a lot of road, and count gear shifts... it should shift 1->2 almost as soon as it starts rolling, then 2-3 around 25mph, and 3->OD(4th) at about 40mph with light throttle. more throttle == higher shift points, of course.